Guys I don't think there's an argument about cranes here but the boom looks proportionally correct to me. If you look on the specs for the barge I think it's 10Te SWL. I won't be r/c'ing my crane but it wouldn't be that hard to do. It will have to be repositionable for access to the deckhouse and the main hatch.
Interestingly half the pictures of the barge show steaming along with the boom fully raised! TBH there's probably not much weight in it and ballasting must take care of it. I presume the crane is that long with the fly jib so that it can load from the quayside or straight onto a ships deck -the lifting radius when slewed out must be relatively short, and ships spares are often not that heavy.
I clean forgot about AIS and there's a fair few more detailed pics on marinetraffic!
Mine's only a passing resemblance but a pic so far is here. I'm not to happy with my crane boom, I think it's too deep and I'll probably shave the bottom of it down a bit.
(sorry, can't get anywhere with PB these days, it won't even let me rotate the pic. Trying to set something else up now).
http://i629.photobucket.com/albums/uu17/RSTA/IMAG2508.jpgCheers,
Rich